There are several reasons why your monitor may not reach your target luminance.

Your monitor is several years old. The native luminance of an older monitor will be lower than a brand new monitor. To check the current maximum luminance, please set the color temperature to its highest value and then measure the luminance within Eye-One Match. This is the maximum cd/m2 that your monitor can output.

Your color temperature target is 5000K or less. When you move the color temperature away from the monitor's native white point, the luminance will also be reduced. If you want to check the maximum possible luminance related to your desired color temperature, adjust the monitor's white point to the target temperature and then measure the maximum luminance with Eye-One Match.

One of the RGB channels has been greatly reduced. Several combinations of R,G,B percentages can lead to the same color temperature. For example: 30% Blue, 70% Green, 80% Red or 50% Blue, 65% Green and 70% Red. For the first example, the desired luminance may not be achieved, because the Blue channel delivers only 30% power. Try to find a combination for the desired color temperature where the RGB percentages are close together.